Add loopback latency test

Add loopback_latency tool to audioloop deps, create a new
audiovideo_LoopabackLatency test to test the latency loop from
playback to capture.

Since this is the initial version of latency test. Right now
the test only examines loopback latency from playback to capture
port through cras alsa plugin. More test configurations will be
added in later changes.

CQ-DEPEND=33435

BUG=chromium-os:32898
TEST=Run audiovideo_LoopbackLatency test passes on Lumpy

Change-Id: I6884a9d7ac779280b4d7b10287162fa5142488e7
Reviewed-on: https://gerrit.chromium.org/gerrit/29413
Commit-Ready: Hsinyu Chao <hychao@chromium.org>
Reviewed-by: Hsinyu Chao <hychao@chromium.org>
Tested-by: Hsinyu Chao <hychao@chromium.org>
5 files changed